Some conventional techniques for modulating polarization for a stereoscopic display are described by Lipton in commonly-owned U.S. Pat. No. 6,975,345 (“Lipton '345”), and by Byatt in U.S. Pat. No. 4,281,341 (“Byatt '341”), both of which are incorporated herein by reference.
In general, Lipton '345 describes a polarizing modulator for use in an electronic stereoscopic display system having a sequentially scanning display that includes a plurality of liquid crystal segments arranged contiguously in a direction of the sequential scan. The liquid crystal material used in each polarization modulation segment has its phase shift tuned in an attempt to minimize the perception of a visible line between segments. Byatt '341 describes a stereoscopic television system that employs a switchable optical polarizer to alternately form images corresponding to the left and right eyes on a television camera. A corresponding switchable polarizer, which comprises a liquid crystal cell containing a thin layer of twisted nematic liquid crystal material, is used in combination with a display device to produce alternating images that are vertically or horizontally polarized. The switchable polarizer associated with the display device is switched in synchronism with the operation of the switchable polarizer associated with the camera.
FIG. 4 is a schematic diagram of a conventional Byatt modulator 401 and FIG. 5 is a schematic waveform diagram illustrating Lipton's known drive scheme for driving a Byatt modulator 401 (shown in FIG. 4), in which the phase shift is tuned by applying a bias voltage to the liquid crystal in its low state. As described therein, Lipton '345 teaches the waveform having portion 501, which has a positive voltage of value +H and portion 503, which has a negative voltage of value −H. In Lipton '345, the device is driven between +H and −H volts (typically between 15 and 20 volts). Lipton '345 teaches driving the shutter at 40 volts peak-to-peak, where +H is 20 volts and −H is −20 volts. Each quarter cycle of the waveform has a duration T and each quarter cycle interval is signified by the designations A, B, C, D. The Byatt modulator 401 is driven to plus or minus H volts for equal durations T. Waveform portions 502 and 504 are defined as the bias voltage. These intervals B and D are of the same duration T as intervals A and C. The bias voltage for intervals B and D have a value of plus and minus L volts, respectively.
Unfortunately, in practice, the technique disclosed in Lipton '345 may, in some circumstances (such as high speed action/motion image sequences), still show slightly perceptible lines between segments of the display device when used with his disclosed scheme.